Chair back



FIG. 1 is a top view of a chair back comprising the new design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a side elevational view thereof; the opposite side elevational view being a mirror image; and,

FIG. 4 is a back elevational view thereof.

The broken lines shown in all views are for illustrative purposes only and form no part of the claimed design. 

The ornamental design for a chair back, as shown and described. 